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bpf: Add bpf_has_frame_pointer() 

Introduce a bpf_has_frame_pointer() helper that unwinders can call to
determine whether a given instruction pointer is within the valid frame
pointer region of a BPF JIT program or trampoline (i.e., after the
prologue, before the epilogue).

This will enable livepatch (with the ORC unwinder) to reliably unwind
through BPF JIT frames.

Acked-by: Song Liu <song@kernel.org>
Acked-and-tested-by: Andrey Grodzovsky <andrey.grodzovsky@crowdstrike.com>
Signed-off-by: Josh Poimboeuf <jpoimboe@kernel.org>
Link: https://lore.kernel.org/r/fd2bc5b4e261a680774b28f6100509fd5ebad2f0.1764818927.git.jpoimboe@kernel.org
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Reviewed-by: Jiri Olsa <jolsa@kernel.org>
master^2
Josh Poimboeuf 2025-12-03 19:32:15 -08:00 committed by Alexei Starovoitov
parent 189e5deb94
commit ca45c84afb
3 changed files with 31 additions and 0 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

12
arch/x86/net/bpf_jit_comp.c
View File

@ -1678,6 +1678,9 @@ static int do_jit(struct bpf_prog *bpf_prog, int *addrs, u8 *image, u8 *rw_image
emit_prologue(&prog, image, stack_depth,
bpf_prog_was_classic(bpf_prog), tail_call_reachable,
bpf_is_subprog(bpf_prog), bpf_prog->aux->exception_cb);
bpf_prog->aux->ksym.fp_start = prog - temp;
/* Exception callback will clobber callee regs for its own use, and
* restore the original callee regs from main prog's stack frame.
*/
@ -2736,6 +2739,8 @@ emit_jmp:
pop_r12(&prog);
}
EMIT1(0xC9); /* leave */
bpf_prog->aux->ksym.fp_end = prog - temp;
emit_return(&prog, image + addrs[i - 1] + (prog - temp));
break;
@ -3325,6 +3330,9 @@ static int __arch_prepare_bpf_trampoline(struct bpf_tramp_image *im, void *rw_im
}
EMIT1(0x55); /* push rbp */
EMIT3(0x48, 0x89, 0xE5); /* mov rbp, rsp */
if (im)
im->ksym.fp_start = prog - (u8 *)rw_image;
if (!is_imm8(stack_size)) {
/* sub rsp, stack_size */
EMIT3_off32(0x48, 0x81, 0xEC, stack_size);
@ -3462,7 +3470,11 @@ static int __arch_prepare_bpf_trampoline(struct bpf_tramp_image *im, void *rw_im
emit_ldx(&prog, BPF_DW, BPF_REG_0, BPF_REG_FP, -8);
emit_ldx(&prog, BPF_DW, BPF_REG_6, BPF_REG_FP, -rbx_off);
EMIT1(0xC9); /* leave */
if (im)
im->ksym.fp_end = prog - (u8 *)rw_image;
if (flags & BPF_TRAMP_F_SKIP_FRAME) {
/* skip our return address and return to parent */
EMIT4(0x48, 0x83, 0xC4, 8); /* add rsp, 8 */

3
include/linux/bpf.h
View File

@ -1283,6 +1283,8 @@ struct bpf_ksym {
struct list_head lnode;
struct latch_tree_node tnode;
bool prog;
u32 fp_start;
u32 fp_end;
};
enum bpf_tramp_prog_type {
@ -1511,6 +1513,7 @@ void bpf_image_ksym_add(struct bpf_ksym *ksym);
void bpf_image_ksym_del(struct bpf_ksym *ksym);
void bpf_ksym_add(struct bpf_ksym *ksym);
void bpf_ksym_del(struct bpf_ksym *ksym);
bool bpf_has_frame_pointer(unsigned long ip);
int bpf_jit_charge_modmem(u32 size);
void bpf_jit_uncharge_modmem(u32 size);
bool bpf_prog_has_trampoline(const struct bpf_prog *prog);

16
kernel/bpf/core.c
View File

@ -760,6 +760,22 @@ struct bpf_prog *bpf_prog_ksym_find(unsigned long addr)
NULL;
}
bool bpf_has_frame_pointer(unsigned long ip)
{
struct bpf_ksym *ksym;
unsigned long offset;
guard(rcu)();
ksym = bpf_ksym_find(ip);
if (!ksym || !ksym->fp_start || !ksym->fp_end)
return false;
offset = ip - ksym->start;
return offset >= ksym->fp_start && offset < ksym->fp_end;
}
const struct exception_table_entry *search_bpf_extables(unsigned long addr)
{
const struct exception_table_entry *e = NULL;